Multi-Epitaxial Layer Substrate for Oxide Field Trench Power MOSFET
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Solution Overview
Problem
Current MOSFET devices face challenges in achieving optimal reverse-biased body-drift diode breakdown and power conduction loss characteristics due to suboptimal epitaxial layer resistivity profiles, leading to inefficient electric field distribution and increased power conduction losses.
Innovation Solution
The implementation of a semiconductor substrate with multiple epitaxial layers, each with distinct thicknesses and doping concentrations, to create a trapezoidal electric field profile, enhancing the breakdown voltage and reducing drain-to-source resistance by modulating the dopant dilute levels during epitaxial growth processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional dual epitaxial layer substrate configuration is used, then the device structure is simpler and manufacturing is easier, but the reverse-biased body-drift diode breakdown voltage is insufficient and power conduction losses are high
Solution Approach 1:
The drift region is segmented into three distinct epitaxial layers (first, second, and third epitaxial layers) with progressively increasing resistivity. This segmentation allows each layer to contribute differently to the electric field distribution, enabling higher breakdown voltage while maintaining controlled power conduction losses. The segmentation transforms a single uniform region into a multi-functional structure that addresses both breakdown and conduction requirements.
Solution Approach 2:
Each epitaxial layer is assigned a specific local quality in terms of resistivity: the first epitaxial layer has lower resistivity to support current conduction, the second epitaxial layer has intermediate resistivity for transition, and the third epitaxial layer has higher resistivity to enhance breakdown voltage. This local quality differentiation creates the desired trapezoidal electric field profile without requiring complex overall device redesign.
2Reliability
If the epitaxial layer resistivity profile is optimized for higher breakdown voltage, then reverse-biased body-drift diode breakdown improves, but power conduction losses increase due to inefficient electric field distribution
Solution Approach 1:
The electric field distribution is made dynamic across the drift region through the three-layer epitaxial structure. Under reverse bias conditions, the high-resistivity third layer dominates to provide high breakdown voltage. Under forward conduction conditions, the lower-resistivity first layer facilitates efficient current flow. This dynamic adaptation to different operating conditions resolves the contradiction between breakdown voltage and conduction losses.
Solution Approach 2:
The resistivity parameter is changed progressively across the three epitaxial layers rather than being uniform. The first epitaxial layer has resistivity ρ1, the second has ρ2 where ρ2 > ρ1, and the third has ρ3 where ρ3 > ρ2. This parameter gradient creates the trapezoidal electric field profile that simultaneously achieves high breakdown voltage and low conduction losses by optimizing the electric field distribution across different regions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration results in improved static performance, including increased breakdown voltage and reduced power conduction losses, with a more than 6% improvement in BVDSS breakdown and over 7% reduction in Rdson compared to traditional dual epi substrate configurations.
Implementation Method 1
create a trapezoidal electric field profile, enhancing the breakdown voltage and reducing drain-to-source resistance
Implementation Method 2
each with distinct thicknesses and doping concentrations, to create a trapezoidal electric field profile
Data Source
AI summary
A semiconductor substrate includes: a base substrate layer doped with a first type dopant; a first epitaxial layer on the base substrate layer that has a first thickness and is doped with the first type dopant to provide a first resistivity; a second epitaxial layer on the first epitaxial layer that has a second thickness and is doped with the first type dopant to provide a second resistivity (less than the third resistivity); and a third epitaxial layer on the second epitaxial layer that has a third thickness and is doped with the first type dopant to provide a third resistivity (less than the second resistivity). An oxide field trench transistor includes a trench with insulated polygate and polysource regions extending into the semiconductor substrate and passing through the first doped region, the second doped region, the third epitaxial layer and partially into the second epitaxial layer.